Zone Precoding

ABSTRACT

Apparatuses, methods, and systems zone precoding are disclosed. One method includes determining a transmission zone for each of the plurality of users, wherein the transmission zone includes an angle of direction of a directional beam to each user, and a deviation of the angle of direction. Determining a precoding of transmission signals to each of the plurality of users from the base station based on the transmission zone associated with the user, and constructing the precoding for each user by adjusting the initial precoding for each user based on the transmission zone determined for each of the other users.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 16/211,014 filed Dec. 5, 2018, which is a continuation of U.S.patent application Ser. No. 15/784,089 filed Oct. 14, 2017 and grantedas U.S. patent application Ser. No. 10,181,880, which are all hereinincorporated by reference.

FIELD OF THE DESCRIBED EMBODIMENTS

The described embodiments relate generally to wireless communications.More particularly, the described embodiments relate to systems, methodsand apparatuses for precoding MIMO (multiple-input, multiple-output)communication signals according to identified zones of users.

BACKGROUND

Massive MIMO (multiple-input, multiple output) systems typically includea large number of antennas. Accordingly, the performance of such systemsis very sensitive to the accuracy of channel knowledge. Further, somemassive MIMO systems, such as implementation using drones or windsensitive high tower deployments suffer from random movements of eitherthe antennas.

It is desirable to have methods apparatuses, and systems for precodingMIMO (multiple-input, multi-output) signals according to identifiedzones of users.

SUMMARY

An embodiment includes a method of zone precoding. The method includesdetermining a precoding of transmission signals to each of a pluralityof users from a base station, and applying the precoding of each user towireless communication signals communicated between the base station andthe user. For an embodiment, the transmission zone includes an angle ofdirection of a directional beam from the base station to each user, anda deviation of the angle of direction of the directional beam. For atleast some embodiments, determining a precoding of transmission signalsto each of the plurality of users from the base station, includesdetermining an initial precoding for each of the users based on thetransmission zone associated with the user, wherein the initialprecoding is selected to provide a received power at the user thatdeviates by less than a threshold over the transmission zone, andconstructing the precoding for each user comprising adjusting theinitial precoding for each user based on the transmission zonedetermined for each of the other users.

Another embodiment includes a base station. The base station includes aplurality of antennas, a plurality of radios connected to the pluralityof antennas, and a controller. The controller operates to determine atransmission zone for each of the plurality of users, wherein thetransmission zone includes an angle of direction of a directional beamto each user from the base station formed by the plurality of antennas,and a deviation of the angle of direction of the directional beam. Thecontroller further operates to determine a precoding of transmissionsignals to each of the plurality of users from the base station based onthe transmission zone determined for each of the other users. Thecontroller further operates to apply the precoding of each user towireless communication signals communicated between the plurality ofantennas of the base station and the user.

Embodiments according to the invention are in particular disclosed inthe attached claims directed to a method and a base station, wherein anyfeature mentioned in one claim category, e.g. method, can be claimed inanother claim category, e.g. base station, system, storage medium, andcomputer program product, as well. The dependencies or references backin the attached claims are chosen for formal reasons only. However anysubject matter resulting from a deliberate reference back to anyprevious claims (in particular multiple dependencies) can be claimed aswell, so that any combination of claims and the features thereof isdisclosed and can be claimed regardless of the dependencies chosen inthe attached claims. The subject-matter which can be claimed comprisesnot only the combinations of features as set out in the attached claimsbut also any other combination of features in the claims, wherein eachfeature mentioned in the claims can be combined with any other featureor combination of other features in the claims. Furthermore, any of theembodiments and features described or depicted herein can be claimed ina separate claim and/or in any combination with any embodiment orfeature described or depicted herein or with any of the features of theattached claims.

In an embodiment according to the invention, a method may comprisetraining a transmission channel between a base station and each of aplurality of users, wherein the base station comprises a plurality ofantennas that operate to form directional beams to each of the pluralityof users, comprising determining a transmission zone for each of theplurality of users, wherein the transmission zone includes an angle ofdirection of a directional beam to each user, and a deviation of theangle of direction, determining a precoding of transmission signals toeach of the plurality of users from the base station, comprisingdetermining an initial precoding for each of the users based on thetransmission zone associated with the user, wherein the initialprecoding is selected to provide a received power at the user thatdeviates by less than a threshold over the transmission zone,constructing the precoding for each user comprising adjusting theinitial precoding for each user based on the transmission zonedetermined for each of the other users, and applying the precoding ofeach user to wireless communication signals communicated between thebase station and the user.

Determining the transmission zone for each of the plurality of users maycomprise determining a direction to the user, determining an indicatorof a stability of the plurality of antennas of the base station.

Determining the transmission zone for each of the plurality of users maycomprises determining a direction to the user, determining a distancebetween the user and the based station, and determining a level ofmobility of the user.

Determining the transmission zone for each of the plurality of users maycomprises determining a cone covariance matrix of radius r for each ofthe users, wherein r is based on the deviation of the angle ofdirection.

Determining the cone covariance matrix may comprise determining everyelement of the cone covariance matrix over the transmission zone,wherein the transmission zone is defined by the direction and radius r.

Determining each element of the cone covariance matrix may comprisedetermining a covariance between pairs of antenna elements n and m overthe transmission zone.

Determining the initial precoding of each user for communication betweenthe base station and each of the users may comprise constructing aninitial precoding vector for each user.

Determining the initial precoding vector for each user may comprise:

determining a dictionary matrix A that includes a set of vectors,wherein each vector of the set of vectors defines a quantized directionin an angular domain; andconstructing initial precoding, using a least square method, for eachuser to ensure a target received power over a set of vectors of thedictionary matrix A that define the transmission zone of the user.

Adjusting the initial precoding for each user based on the transmissionzone determined for each of the other users may comprise determining aninterference nulling matrix for the user for the transmission zones ofother users.

Determining the interference nulling matrix may include determiningsubspaces of the interference nulling matrix to ensure that a signaltransmitted by the user does not cause interference in transmissionzones of the other users.

Determining the precoding may comprise determining a precoding matrix,wherein the precoding matrix may include a precoding vector for eachuser.

Determining the precoding matrix may comprise constructing the precodingvector for each user by projecting an initial precoding vector of theuser on interference nulling matrices of the other users.

In an embodiment according to the invention, a base station may comprisea plurality of antennas, a plurality of radios connected to theplurality of antennas, a controller, wherein the controller operates todetermine a training of a transmission channel between the plurality ofantennas of the base station and each of a plurality of users, whereinthe plurality of antennas operate to form directional beams to each ofthe plurality of users, comprising determining a transmission zone foreach of the plurality of users, wherein the transmission zone includesan angle of direction of a directional beam to each user, and adeviation of the angle of direction, determine a precoding oftransmission signals to each of the plurality of users from the basestation, comprising determine an initial precoding for each of the usersbased on the zone associated with the user, wherein the initialprecoding is selected to provide a received power over the transmissionzone of the user that deviates by less than a threshold, and constructthe precoding for each user comprising adjusting the initial precodingfor each user based on the transmission zone determined for each of theother users, and apply the precoding of each user to wirelesscommunication signals communicated between the plurality of antennas ofthe base station and the user.

Determining the transmission zone for each of the plurality of users maycomprise determining a cone covariance matrix of radius r for each ofthe users, wherein r is based on the deviation of the angle ofdirection, and wherein determining the cone covariance matrix comprisesdetermining each element of the cone covariance matrix over thetransmission zone, wherein the transmission zone is defined by thedirection and radius r, wherein determining each element of the conecovariance matrix comprises determining a covariance between pairs ofantenna elements n and m over the transmission zone.

Determining the initial precoding of each user for communication betweenthe base station and each of the users may comprise constructing aninitial precoding vector for each user, which may comprise determining adictionary matrix A that includes a set of vectors, wherein each vectorof the set of vectors defines a quantized direction in an angulardomain; and constructing initial precoding, using a least square method,for each user to ensure a target received power over a set of vectors ofthe dictionary matrix A that define the transmission zone of the user.

Adjusting the initial precoding for each user based on the transmissionzone determined for each of the other users may comprise determining aninterference nulling matrix for the user for the transmission zones ofother users.

Determining the interference nulling matrix may include determiningsubspaces of the interference nulling matrix to ensure that a signaltransmitted by the user does not cause interference in transmissionzones of the other users.

Determining the precoding may comprise determining a precoding matrix,wherein the precoding matrix may include a precoding vector for eachuser.

Determining the precoding matrix may comprise constructing the precodingvector for each user by projecting an initial precoding vector of theuser on interference nulling matrices of the other users.

In an embodiment according to the invention, a method may comprise:

training a transmission channel between a base station and each of aplurality of users, wherein the base station comprises a plurality ofantennas that operate to form directional beams to each of the pluralityof users, comprising determining a transmission zone for each of theplurality of users, wherein the transmission zone includes an angle ofdirection of a directional beam to each user, and a deviation of theangle of direction, selecting a precoding of transmission signals toeach of the plurality of users from the base station to provide areceived power that deviates by less than a threshold over thetransmission zone, and wherein received interference within transmissionzones of other users is below a threshold, and applying the precoding ofeach user to wireless communication signals between the base station andthe user.

In an embodiment according to the invention, one or morecomputer-readable non-transitory storage media may embody software thatis operable when executed to perform a method according to the inventionor any of the above mentioned embodiments.

In an embodiment according to the invention, a system may comprise: oneor more processors; and at least one memory coupled to the processorsand comprising instructions executable by the processors, the processorsoperable when executing the instructions to perform a method accordingto the invention or any of the above mentioned embodiments.

In an embodiment according to the invention, a computer program product,preferably comprising a computer-readable non-transitory storage media,may be operable when executed on a data processing system to perform amethod according to the invention or any of the above mentionedembodiments.

Other aspects and advantages of the described embodiments will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a system that includes a base station having M antennasthat communicates with K single-antenna users, according to anembodiment.

FIG. 2 shows a system that includes a base station having M antennasthat communicates with K single-antenna users, wherein precoding ofcommunication with K users is based on identified zones of the K users,according to an embodiment.

FIG. 3 shows a base station having M antennas, wherein precoding ofcommunication with users is based on identified zones of the users,according to an embodiment.

FIG. 4 is a flow chart that includes acts of a method of zone precoding,according to an embodiment.

FIG. 5 is a flow chart that includes acts of a method of zone precoding,according to another embodiment.

FIG. 6 shows simulated results of a MIMO transmitter, according to anembodiment.

FIG. 7 shows simulated results of a MIMO transmitter, according to anembodiment.

DETAILED DESCRIPTION

The embodiments described include methods, apparatuses, and systems forprecoding signals communicated between a base station having multipleantennas and multiple users, wherein the precoding is selected based onzones associated with each of the multiple users.

At least some of the described embodiments provide robustness inachievable rates of data transmission when challenged with user mobilityand random angle perturbation (due, for example, to motion of antennas).This is particularly important for massive MIMO and mmWave MIMO systemswhere large numbers of antennas are deployed and where the performanceis very sensitive to accurate channel knowledge. Further, the describedembodiments are useful for systems that suffer from random movementssuch as drones and wind-sensitive high-tower deployments.

FIG. 1 shows a system that includes a base station 120 having M antennasthat communicates with K single-antenna users 132, 134, 136, accordingto an embodiment. While shown and described as single-antenna users, itis to be understood that the described embodiments are applicable tomultiple antenna users as well. For at least some embodiments, in thedownlink transmission, the base station 120 employs a precoding matrix Fto transmit symbols s to the K users 132, 134, 136. The received signalat every user k, k=1, . . . , K can be written as:

r ^(k) =h _(k) *Fs+n _(k)

where h_(k) is an M×1 channel vector of the k-th user and the transmitsignal is normalized so that

${{E\begin{bmatrix}s & s^{*}\end{bmatrix}} = {\frac{P}{K}\mspace{14mu} I}},$

with a total transmit power of P.

The transmission channel between the base station 120 and the K users132, 134, 136 can be modeled by a channel estimate (H=[h₁, . . . ,h_(K)]) 150. For at least some embodiments, the channel estimate H isdetermined by training of the transmission channel between the basedstation 120 and the users. For an embodiment, the training includestransmitting known signals (symbols) between the base station and theusers, and observing the received signals.

As will be described, for at least some embodiments, the transmissionchannel H between the base station 120 and the users 132, 134, 136 isretrained. For an embodiment, the training is performed periodically.For an embodiment, the period is selected based on a mobility of theuser, sensed location changes of the user, or a stability of antennas ofthe base station. For at embodiment, the training is performed notperiodically, but based on sensing a condition. For an embodiment, thecondition for performing the training is based on a mobility of theuser, sensed location changes of the user, or a stability of antennas ofthe base station.

For a line-of-sight (LOS) channel model, a channel for every user can beconstructed as an array response vector that corresponds with an angleof departure (AoD) associated with the location of the user. Accordingto this channel model, the channel of user k=1, . . . , K can beexpressed as:

$h_{k} = \left\lbrack {1,{\exp \mspace{14mu} \left( {{j\frac{2{\pi d}}{\lambda}\mspace{14mu} \cos \mspace{14mu} \left( \theta_{k} \right)},{\exp \mspace{11mu} j\mspace{11mu} 2\frac{2{\pi d}}{\lambda}\mspace{11mu} d\mspace{11mu} \cos \mspace{11mu} \left( \theta_{k} \right)},\ldots \mspace{14mu},{\exp \mspace{14mu} \left( {j\mspace{11mu} \left( {M - 1} \right)\frac{2{\pi d}}{\lambda}\mspace{11mu} d\mspace{11mu} \cos \mspace{11mu} \left( \theta_{k} \right)} \right)},} \right.}} \right.$

where (θ_(k)) is the angle of direction (AoD) of user k, d is thespacing between the antenna elements, and λ is the wavelength.

FIG. 2 shows a system that includes a base station 120 having M antennasthat communicates with K single-antenna users 132, 134, 136, whereinprecoding of communication with K users is based on identified zones142, 144, 146 of the K users, according to an embodiment. The pluralityof M antennas of the base station operates to form directional beams toeach of the plurality of users.

At least some embodiments include identifying transmission zones foreach of the K users by training the transmission channel between thebase station and each of a plurality of K users. For at least someembodiments, the training includes determining a transmission zone foreach of the plurality of users, wherein the transmission zone includesdetermining an angle of direction of a directional beam to each user,and a deviation of the angle of direction.

After the transmission zone for each of the plurality of users has beendetermined, an embodiment includes determining a precoding oftransmission signals to each of the plurality of users from the basestation. For at least some embodiments, determining the precodingincludes determining an initial precoding for each of the users based onthe transmission zone associated with the user, wherein the initialprecoding is selected to provide a received power at the user thatdeviates by less than a threshold over the transmission zone. That is,the initial precoding is selected to maintain a near-constant level ofreceived power across the transmission zone of the user.

Once the initial precoding for each of the users has been determined,the effect of each of the users on each of the other users isdetermined. That is, the initial precoding for each user forms adirectional beam directed to each of the transmission zones of each ofthe users. However, directionally formed beams naturally include sidelobes. The side lobes of each of the directional beams of each user maycause interference with other of the users. For an embodiment, theinitial precoding for each user is adjusted or modified to reduce theeffects of side lobe energy of the directional beam of the user on otherof the users. That is, for an embodiment, constructing the precoding foreach user includes adjusting the initial precoding for each user basedon the transmission zone determined for each of the other users.Further, the initial precoding for each of the users is adjusted toreduce the impact of the transmission between the base station and eachuser on the other users. That is, the initial precoding for a user isselected to ensure a near-constant level of received power over thetransmission zone of the user, and the precoding is selected by updatingor adjusting the initial precoding to reduce (or eliminate) the impactthe precoding of each user has on the transmission zones of the otherusers.

Once the precoding has been determined, the precoding is applied of eachuser to wireless communication signals communicated between the basestation and the user.

Transmission Zones

As described, for an embodiment, the transmission zone of each of theusers is determined or defined by the angle of direction of adirectional beam to each user, and a deviation of the angle ofdirection. Factors that can influence the transmission zone selection ordetermination include a stability of one or more of the plurality ofantennas of the base station, or a mobility of the user. That is, ifeither the one or more of the plurality of antennas of the base station,or the antenna of the user are prone to movement, then the transmissionzone may be accordingly increased in size depending upon the level ordegree of movement. The transmission zones for the different users canbe of varying sizes.

As previously described, for an embodiment, the transmission zone ofeach of the users is determined during the channel training. Also, aspreviously described, for an embodiment, the transmission channelbetween the base station 120 and the users 132, 134, 136 is retrained,which can yield a revised or new angle of direction of the directionalbeam to one or more of the users, and a new or revised deviation of theangle of direction to the one or more of the users. For an embodiment,the training is performed periodically. For an embodiment, the period isselected based on a mobility of the user, sensed location changes of theuser, or a stability of antennas of the base station. For at embodiment,the training is performed based on sensing a condition. For anembodiment, the condition sensed for performing the training is based ona mobility of the user, sensed location changes of the user, or astability of antennas of the base station.

Alternatively or additionally, the transmission zone for each of theplurality of users can be influenced by the distance between the userand the base station, and/or a level of mobility of the user. That is,the farther the user is away from the base station, the more sensitivethe system is to motion of either the base station or the user(s).Therefore, for user mobility, the size of the transmission zone can bedecreased as the distance between the base station and the user isincreased. However, for perturbations or vibrations in the antennaelements, the size of the transmission zone can be increased as thedistance between the base station and the user is increased.

Further, size of the transmission zone can be increased as the mobilityof the user increases. That is, a mobile user changes location. The moremobile the user is, the more rapidly the location changes. For at leastsome embodiments, the size of the transmission zone is selected based atleast in part on a level of mobility of the user.

For at least some embodiments determining the transmission zone for eachof the plurality of users includes determining a cone covariance matrixof radius r for each of the users, wherein r is based on the deviationof the angle of direction (the radius r for the transmission zone ofUser 1 is shown in FIG. 2). The greater the deviation in the angle ofdirection, the greater the size of the transmission zone, and the radiusr of the transmission zone.

For at least some embodiments, determining the cone covariance matrixincludes determining each element of the cone covariance matrix over thetransmission zone, wherein the transmission zone is defined by thedirection and radius r. For at least some embodiments, determining eachelement of the cone covariance matrix includes determining a covariancebetween pairs of antenna elements n and m over the transmission zone.That is each element of the channel covariance matrix is given by thecovariance computed over the transmission zone defined by direction andradius between any pair of antennas at the base station for each antennapair of the plurality of antennas of the base station.

For at least some embodiments, determining the cone covariance matrixincludes calculating the cone covariance matrix [R_(k)]_(m,n) asfollows:

${\left\lbrack R_{k} \right\rbrack_{m,n} = {\int_{- r}^{r}{\exp \mspace{14mu} \left( {{j\left( \frac{2\pi}{\lambda} \right)}\left( {m - n} \right)\mspace{14mu} \cos \mspace{11mu} \left( {\left( \theta_{k} \right) + \delta} \right)} \right)\mspace{11mu} d\; \delta}}},$

where [R_(k)]_(m,n) is the element of the cone covariance matrix R_(k)at the m-th row and the n-th column. Further, for a user k, (θ_(k)) isthe angle of direction of the user, δ is the deviation angular directionof the user, and λ is the wavelength of the electromagnetic signalcommunicated between the base station and the user, and r is the radiusof the transmission zone at the user k.

For at least some embodiments, the cone covariance matrices of the Kusers define sub-spaces of the zones/regions around each of the K users.

-   -   Initial Precoding

As previously described, for at least some embodiments, the initialprecoding is selected to provide a received power at the user thatdeviates by less than a threshold over the transmission zone. That is,the initial precoding is selected to maintain a near-constant level ofreceived power across the transmission zone.

For at least some embodiments, determining the initial precoding of eachuser for communication between the base station and each of the usersincludes constructing an initial precoding vector for each user. For anembodiment, determining the initial precoding vector for each userincludes determining a dictionary matrix A that includes a set ofvectors, wherein each vector of the set of vectors defines a quantizeddirection in an angular domain, and constructing initial precoding,using a least square method, for each user to ensure a target receivedpower over a set of vectors of the dictionary matrix A that define thetransmission zone of the user. The method of least squares is a standardapproach in regression analysis to an approximate solution ofoverdetermined systems. That is, sets of equations in which there aremore equations than unknowns. For a given A, initial precoding isconstructed for each user k to ensure a target received power over setof vectors of A that define the transmission zone of the user using theleast squared method.

For at least some embodiment, determining the initial precoding vectorfor each user include computing the initial precoding vector (alsoreferred to as an equivalent channel vector)

includes:

-   -   Where A^(†) is the pseudo-inverse of the matrix A, and A is the        previously described dictionary matrix, wherein columns of the        dictionary matrix are an array response of vectors of uniformly        quantized angles in a range [0, 180], and

p _(k)=diag(A*[U _(k)]_(:,1:rank(Rk)) [U _(k)]*_(:,1:rank(Rk)) A)

-   -   where U_(k) is a matrix that gathers (includes) the left        singular vectors of R_(k), and results from a singular value        decomposition (SVD) of R_(k)=U_(k)S_(k)V_(k)

For at least some embodiments, the initial precoding vector

is constructed so that projections of the initial precoding vector

on the columns of the dictionary matrix A is approximately equal to thesum of the power of the projections of [U_(k)]_(:,1:rank(Rk)) on thecolumns of the dictionary matrix A.

-   -   Precoding

As previously described, for at least some embodiment, the precoding isdetermined or constructed by adjusting or updating the initialprecoding. That is, the effects of the initial precoding of each user onthe transmission zones other users, is used to adjust the initialprecoding. That is, interference (due, for example, to side lobes)caused the initial precoding of a user within the transmission zones ofthe other users is used adjust the precoding of the user.

For at least some embodiments, adjusting the initial precoding for eachuser based on the transmission zone determined for each of the otherusers comprises determining an interference nulling matrix. For at leastsome embodiments, determining the interference nulling matrix includesdetermining subspaces of the interference nulling matrix to ensure thata signal transmitted by the user does not cause interference intransmission zones of the other users.

For at least some embodiments, determining the precoding comprisesdetermining a precoding matrix, wherein the precoding matrix includes aprecoding vector for each user. For at least some embodiments,determining the precoding matrix comprises constructing the precodingvector for each user by projecting an initial precoding vector of theuser on interference nulling matrices of the other users.

For an embodiment, the precoding of the base station includesdetermining a precoding matrix F as:

-       where    is an M×K equivalent channel matrix that includes the equivalent    channel vectors (columns) of the K users, and where P is an    interference projection matrix.

For at least some embodiments, the interference matrix P is determinedas follows:

P=[U ₁ ^(Null) ,U ₂ ^(Null) , . . . ,U _(K) ^(Null)],

wherein for an embodiment, U_(k) ^(Null) is a matrix that representsleft singular vectors of the null-space of a matrix that results fromsumming the cone covariance matrices of all the users except user k.

FIG. 3 shows a base station 120 having M antennas, wherein precoding ofcommunication with users is based on identified zones of the users,according to an embodiment. As shown, the base station 120 includes acontroller 350, zone precoding 380, M radios 321, 328, and M antennas(Ant1, AntM). The M antennas operate to form directional beams to Kusers. The precoding of the zone precoder 380 is selected to form atransmission zone for each of the K users.

For at least some embodiments, the controller 350 operates to determinea training of a transmission channel between the plurality of antennasof the base station and each of a plurality of users, wherein theplurality of antennas operate to form directional beams to each of theplurality of users, comprising determining a transmission zone for eachof the plurality of users, wherein the transmission zone includes anangle of direction of a directional beam to each user, and a deviationof the angle of direction. Further, the controller 350 is operative todetermine a precoding of transmission signals to each of the pluralityof users from the base station, including determine an initial precodingfor each of the users based on the zone associated with the user,wherein the initial precoding is selected to provide a received powerover the transmission zone of the user that deviates by less than athreshold, and construct the precoding for each user comprisingadjusting the initial precoding for each user based on the transmissionzone determined for each of the other users. Further, the controller 350is operative to apply the precoding of each user to wirelesscommunication signals communicated between the plurality of antennas ofthe base station and the user.

FIG. 4 is a flow chart that includes acts of a method of zone precoding,according to an embodiment. A first step 410 includes training atransmission channel between a base station and each of a plurality ofusers, wherein the base station comprises a plurality of antennas thatoperate to form directional beams to each of the plurality of users. Forat least some embodiments, training a transmission channel between abase station and each of a plurality of users comprises determining atransmission zone for each of the plurality of users, wherein thetransmission zone includes an angle of direction of a directional beamto each user, and a deviation of the angle of direction. A second step420 includes determining a precoding of transmission signals to each ofthe plurality of users from the base station. For at least someembodiments, determining the precoding of transmission signals to eachof the plurality of users from the base station comprises determining aninitial precoding for each of the users based on the transmission zoneassociated with the user, wherein the initial precoding is selected toprovide a received power at the user that deviates by less than athreshold over the transmission zone, and constructing the precoding foreach user comprising adjusting the initial precoding for each user basedon the transmission zone determined for each of the other users. A thirdstep 430 includes applying the precoding of each user to wirelesscommunication signals between the base station and the user.

As previously described, for an embodiment, determining the transmissionzone for each of the plurality of users includes determining a directionto the user, determining an indicator of \a stability of the pluralityof antennas of the base station. As previously described, for anembodiment, determining the transmission zone for each of the pluralityof users comprises determining a direction to the user, determining adistance between the user and the based station, and determining a levelof mobility of the user.

As previously described, for an embodiment, determining the transmissionzone for each of the plurality of users comprises determining a conecovariance matrix of radius r for each of the users, wherein r is basedon the deviation of the angle of direction. As previously described, foran embodiment, determining the cone covariance matrix comprisesdetermining every element of the cone covariance matrix over thetransmission zone, wherein the transmission zone is defined by thedirection and radius r. As previously described, for an embodiment,determining each element of the cone covariance matrix comprisesdetermining a covariance between pairs of antenna elements n and m overthe transmission zone.

As previously described, for an embodiment, determining the initialprecoding of each user for communication between the base station andeach of the users comprises constructing an initial precoding vector foreach user. For an embodiment, determining the initial precoding vectorfor each user includes determining a dictionary matrix A that includes aset of vectors, wherein each vector of the set of vectors defines aquantized direction in an angular domain, and constructing initialprecoding, using a least square method, for each user to ensure a targetreceived power over a set of vectors of the dictionary matrix A thatdefine the transmission zone of the user.

As previously described, for an embodiment, adjusting the initialprecoding for each user based on the transmission zone determined foreach of the other users comprises determining an interference nullingmatrix for the user for the transmission zones of other users. For anembodiment, determining the interference nulling matrix includesdetermining subspaces of the interference nulling matrix to ensure thata signal transmitted by the user does not cause interference intransmission zones of the other users.

As previously described, for an embodiment, determining the precodingcomprises determining a precoding matrix, wherein the precoding matrixincludes a precoding vector for each user. For an embodiment,determining the precoding matrix comprises constructing the precodingvector for each user by projecting an initial precoding vector of theuser on interference nulling matrices of the other users.

FIG. 5 is a flow chart that includes acts of a method of zone precoding,according to another embodiment. A first step 510 includes training atransmission channel between a base station and each of a plurality ofusers, wherein the base station comprises a plurality of antennas thatoperate to form directional beams to each of the plurality of users,include determining a transmission zone for each of the plurality ofusers, wherein the transmission zone includes an angle of direction of adirectional beam to each user, and a deviation of the angle ofdirection. A second step 520 includes selecting a precoding oftransmission signals to each of the plurality of users from the basestation to provide a received power that deviates by less than athreshold over the transmission zone, and wherein received interferencewithin transmission zones of other users is below a threshold. A thirdstep 530 includes applying the precoding of each user to wirelesscommunication signals between the base station and the user.

For this embodiment, the precoding is selected to ensure thattransmission signals to each of the plurality of users from the basestation to provide a received power that deviates by less than athreshold over the transmission zone, and received interference withintransmission zones of other users is below a threshold. For an alternateembodiment, the precoding is selected to ensure that receivedinterference within transmission zones of other users is below athreshold. The precoding is then adjusted or selected to ensure thattransmission signals to each of the plurality of users from the basestation to provide a received power that deviates by less than athreshold over the transmission zone.

FIG. 6 shows simulated results of a MIMO transmitter, according to anembodiment. This simulated MIMO includes 100 antennas communicating with5 users. For the simulation, the users are randomly located on ahalf-circle. That is, the angle of directions (AoD)s of each user israndomly selected from [0, 180] degrees. The achievable rate per-user ofconventional zero-forcing [where the precoder is constructed as F=H^(†)]versus the protected-zone precoding of the described embodiments (bothof them are normalized such that the columns have unit norm) isillustrated in FIG. 6.

From FIG. 6, is can be observed that when the perturbation angle islarge, the described embodiments for zone precoding provide improvedgain as compared to conventional zero-forcing precoding. Further, thesimulation shows that the described embodiments for zone precodingprovide almost constant performance (within a threshold) regardless ofthe perturbation angle.

FIG. 7 shows simulated results of a MIMO transmitter, according to anembodiment. This embodiment shows the achievable rate of the describedembodiments for zone precoding compared to zero-forcing for differentnumber of users (2 users or 6 users), wherein the number of base stationantennas is fixed at 100, the cone zone is 2 degrees, and theperturbation angle is 2 degrees. FIG. 7 shows that the describedembodiments that include protected-zone precoding provide a good gain(within a threshold) over conventional zero-forcing when the number ofusers is low compared to the number of antennas (this setup has 100antennas). Note that the gain increases as the number of antennasincreases.

Although specific embodiments have been described and illustrated, theembodiments are not to be limited to the specific forms or arrangementsof parts so described and illustrated. The described embodiments are toonly be limited by the claims.

1. A method, comprising: determining a transmission zone for each of aplurality of users, wherein the transmission zone includes an angle ofdirection of a directional beam from a base station to each user, and adeviation of the angle of direction of the directional beam; determininga precoding of transmission signals to each of the plurality of usersfrom the base station, comprising: constructing the precoding for eachuser based on the transmission zone determined for each of other usersof the plurality of users; and applying the precoding of each user towireless communication signals communicated between the base station andthe user.
 2. The method of claim 1, further comprising: determining aninitial precoding for each of the users based on the transmission zoneassociated with the user; and wherein constructing the precoding foreach user comprises adjusting the initial precoding for each user basedon the transmission zone determined for each of the other users.
 3. Themethod of claim 2, wherein the initial precoding is selected to providea received power at the user that deviates by less than a threshold overthe transmission zone.
 4. The method of claim 1, wherein determining thetransmission zone for each of the plurality of users comprisesdetermining a direction to the user, determining an indicator of astability of the plurality of antennas of the base station.
 5. Themethod of claim 1, wherein determining the transmission zone for each ofthe plurality of users comprises determining a direction to the user,determining a distance between the user and the based station, anddetermining a level of mobility of the user.
 6. The method of claim 1,wherein determining the transmission zone for each of the plurality ofusers comprises determining a cone covariance matrix of radius r foreach of the users, wherein r is based on the deviation of the angle ofdirection.
 7. The method of claim 6, wherein determining the conecovariance matrix comprises determining every element of the conecovariance matrix over the transmission zone, wherein the transmissionzone is defined by the direction and radius r.
 8. The method of claim 7,wherein determining each element of the cone covariance matrix comprisesdetermining a covariance between pairs of antenna elements n and m overthe transmission zone.
 9. The method of claim 2, wherein determining theinitial precoding of each user for communication between the basestation and each of the users comprises constructing an initialprecoding vector for each user.
 10. The method of claim 9, whereindetermining the initial precoding vector for each user comprises:determining a dictionary matrix A that includes a set of vectors,wherein each vector of the set of vectors defines a quantized directionin an angular domain; and constructing initial precoding, using a leastsquare method, for each user to ensure a target received power over aset of vectors of the dictionary matrix A that define the transmissionzone of the user.
 11. The method of claim 2, wherein adjusting theinitial precoding for each user based on the transmission zonedetermined for each of the other users comprises determining aninterference nulling matrix for the user for the transmission zones ofother users.
 12. The method of claim 11, wherein determining theinterference nulling matrix includes determining subspaces of theinterference nulling matrix to ensure that a signal transmitted by theuser does not cause interference in transmission zones of the otherusers.
 13. The method of claim 12, wherein determining the precodingcomprises determining a precoding matrix, wherein the precoding matrixincludes a precoding vector for each user.
 14. A base station,comprising: a plurality of antennas; a plurality of radios connected tothe plurality of antennas; a controller, wherein the controller operatesto: determine a transmission zone for each of a plurality of users,wherein the transmission zone includes an angle of direction of adirectional beam to each user from the base station formed by theplurality of antennas, and a deviation of the angle of direction of thedirectional beam; determine a precoding of transmission signals to eachof the plurality of users from the base station, comprising:constructing the precoding for each user based on the transmission zonedetermined for each of the other users; and apply the precoding of eachuser to wireless communication signals communicated between theplurality of antennas of the base station and the user.
 15. The basestation of claim 14, wherein the controller further operates to:determine an initial precoding for each of the users based on thetransmission zone associated with the user; and wherein constructing theprecoding for each user comprises adjusting the initial precoding foreach user based on the transmission zone determined for each of theother users.
 16. The base station of claim 15, wherein the initialprecoding is selected to provide a received power over the transmissionzone of the user that deviates by less than a threshold.
 17. The basestation of claim 14, wherein determining the transmission zone for eachof the plurality of users comprises determining a cone covariance matrixof radius r for each of the users, wherein r is based on the deviationof the angle of direction, and wherein determining the cone covariancematrix comprises determining each element of the cone covariance matrixover the transmission zone, wherein the transmission zone is defined bythe direction and radius r, wherein determining each element of the conecovariance matrix comprises determining a covariance between pairs ofantenna elements n and m over the transmission zone.
 18. The basestation of claim 15, wherein determining the initial precoding of eachuser for communication between the base station and each of the userscomprises constructing an initial precoding vector for each user,comprising: determining a dictionary matrix A that includes a set ofvectors, wherein each vector of the set of vectors defines a quantizeddirection in an angular domain; and constructing initial precoding,using a least square method, for each user to ensure a target receivedpower over a set of vectors of the dictionary matrix A that define thetransmission zone of the user.
 19. The base station of claim 15, whereinadjusting the initial precoding for each user based on the transmissionzone determined for each of the other users comprises determining aninterference nulling matrix for the user for the transmission zones ofother users.
 20. The base station of claim 19, wherein determining theinterference nulling matrix includes determining subspaces of theinterference nulling matrix to ensure that a signal transmitted by theuser does not cause interference in transmission zones of the otherusers.